Utilization of Recycled Materials in Illinois Highway Construction

Air-Cooled Blast Furnace Slag

Origin:

Iron ore, as well as scrap iron, is reduced to a molten state by burning coke fuel with fluxing agents of limestone and/or dolomite. Simultaneously during the iron production, slag is developed in the blast furnace. Air-Cooled Blast Furnace Slag (ACBFS), one of various slag products, is formed when the liquid slag is allowed to cool under atmospheric conditions. It may later be broken down with typical aggregate processing equipment to meet gradation specifications (1).

Physical Properties:

ACBFS is a hard, angular material with textures ranging from rough, porous surfaces to smooth, shell-like fractured surfaces. Though vesicular, the structure's cells are not inter-connected and little absorption to the interior is likely. Physical properties (e.g. unit weight and size) can vary considerably depending on the method of production; for example, high use of scrap iron can lead to higher unit weights (1, 2).

Engineering Value:

Crushed ACBFS can be used in nearly all applications utilizing natural aggregates, such as bituminous and portland cement concretes, embankments, or subbases. ACBFS has potentially favorable resistance to polishing, weathering durability, and bearing. However, the material's inherent variability in physical properties can be of concern. For example, included in bituminous concrete pavements, this material provides exceptional frictional properties and increased stability, but its tendency for high surface absorption may require greater amounts of asphalt binder (1, 2).

Present Application:

ACBFS is incorporated into portland cement concrete (PCC), bituminous concrete, granular bases and subbases, embankments, and fills. As of August 1999, a self-testing producer control program had been added to specifications regarding bituminous concrete mixes. For the most part, slag is tested as though it were a natural aggregate; unless the application pertains to bituminous concrete, IDOT will not use slag failing LA Abrasion test limits (3).